Variable engine valve actuator

ABSTRACT

An engine valve actuation system is provided. The system includes an engine valve having a valve element, a rocker arm having a pivot point, a first end, and a second end, and a valve actuator. The valve actuator has a body member having a chamber adapted to receive a fluid, a seat, and a passageway adapted to conduct fluid into and out of the chamber. A piston is slidably disposed in the chamber of the body member and is operatively engaged with the second end of the rocker arm. A control valve is connected to the passageway. The control valve has a first position where fluid is allowed to flow relative to the passageway to allow the body member to move relative to the piston until the seat moves into engagement with the piston to thereby move the piston to pivot the rocker arm and actuate the engine valve. The control valve also has a second position where fluid is prevented from flowing relative to the passageway so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and actuate the engine valve while the piston is separated from the seat by an amount of fluid.

TECHNICAL FIELD

[0001] The present invention is directed to an engine valve actuation system and, more particularly, to a variable valve actuation system for an internal combustion engine.

BACKGROUND

[0002] An internal combustion engine typically includes a series of valves that are configured to control the intake and exhaust of gases to and from the engine. A typical engine will include at least one intake valve and at least one exhaust valve for each combustion chamber in the engine. The opening of each valve is typically timed to occur at a certain point in the operating cycle of the engine. For example, an intake valve may be opened when a piston is moving towards a bottom dead center position within a cylinder to allow fresh air to enter the combustion chamber. An exhaust valve may be opened when the piston is moving towards a top dead center position in the cylinder to expel exhaust gas from the combustion chamber.

[0003] The efficiency and emission generation characteristics of the engine may be improved by varying the actuation timing of the intake and/or exhaust valves to meet different engine operating conditions. For example, when the vehicle is reducing speed, the exhaust valve actuation timing may be varied to implement an “engine braking” cycle. Engine braking involves opening the exhaust valves when the piston is approaching the top dead center position of a compression stroke to release compressed gas from the combustion chamber instead of inducing combustion. In this manner, the kinetic energy of the moving vehicle may be dissipated by compressing the gas in the compression chamber, which results in a slowing, or “braking,” of the engine.

[0004] The actuation timing of the intake valves may also be varied to improve the performance of the engine when the engine is experiencing certain operating conditions. For example, a “late intake Miller cycle” may be implemented when the engine is experiencing steady state conditions. A late intake Miller cycle involves holding the intake valves open as the piston moves through an intake stroke and for a first portion of the compression stroke. The late intake Miller cycle may lead to improved engine efficiency and/or reduced emission generation.

[0005] To obtain these types of improvements in engine performance, the engine requires a valve actuation system that adjusts the valve actuation timing based on the current operating conditions of the engine. For example, when it is determined that the engine is operating in steady-state conditions, the valve actuation system may vary the actuation timing of the intake valves to implement the late intake Miller cycle. Because the engine operating conditions may change frequently, the valve actuation system should be capable of quickly responding and varying the valve actuation timing to meet the current engine operating conditions.

[0006] Engine valves are typically actuated by either a cam driven system or a hydraulic system. In a conventional cam driven system, a cam having one or more cam lobes is rotated in conjunction with the engine crankshaft to actuate the engine valves. The shape of the cam lobes determines the valve actuation timing. This type of system is relatively inflexible as the timing of the engine valves will be remain constant regardless of the vehicle operating conditions.

[0007] In a hydraulic system, a pressurized fluid is used to actuate the engine valves. A hydraulically driven system is typically more flexible than a cam driven system because the actuation timing of a hydraulic system is independent of crankshaft rotation. However, a hydraulic system typically requires additional components, such as a high pressure pump and a complex control system. These additional components may significantly increase the cost of the valve actuation system and the amount of maintenance required on the engine.

[0008] A valve actuation system may use a combination of cams and hydraulics that allow the valve actuation timing to be varied in response to different operating conditions. For example, as described in U.S. Pat. No. 6,415,752 to Janak, issued on Jul. 9, 2002, a rotating cam assembly may drive a master and slave piston assembly to actuate an engine valve. A lost motion device may be disposed between the master and slave pistons to allow the actuation of the engine valve to be varied based on the amount of fluid within the lost motion device. However, this type of system requires a fluid link between the master piston, which is engaged with the cam assembly, and the slave piston, which is engaged with the engine valve. Providing this fluid link may require complex and expensive components.

[0009] The engine valve actuation system of the present invention solves one or more of the problems set forth above.

SUMMARY OF THE INVENTION

[0010] In one aspect, the present invention is directed to an engine valve actuation system that includes an engine valve having a valve element, a rocker arm having a pivot point, a first end, and a second end, and a valve actuator. The valve actuator has a body member having a chamber adapted to receive a fluid, a seat, and a passageway adapted to conduct fluid into and out of the chamber. A piston is slidably disposed in the chamber of the body member and is operatively engaged with the second end of the rocker arm. A control valve is connected to the passageway. The control valve has a first position where fluid is allowed to flow relative to the passageway to allow the body member to move relative to the piston until the seat moves into engagement with the piston to thereby move the piston to pivot the rocker arm and actuate the engine valve. The control valve also has a second position where fluid is prevented from flowing relative to the passageway so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and actuate the engine valve while the piston is separated from the seat by an amount of fluid.

[0011] In another aspect, the present invention is directed to a method of actuating a valve in an engine. A cam assembly is operated to move a body member between a first position and a second position. The body member has a chamber adapted to slidably receive a piston that is operatively connected to a valve element through a rocker arm. A fluid is directed into the chamber in the body member. An operating parameter of the engine is sensed. The fluid is prevented from leaving the chamber when the sensed operating parameter indicates that the engine is experiencing a first operating condition. The fluid in the chamber links the body member with the piston so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and thereby actuate the valve. The fluid is allowed to leave the chamber when the sensed operating parameter indicates that the engine is experiencing a second operating condition. The escaping fluid allows the body member to move relative to the piston until the seat engages the piston to pivot the rocker arm and thereby actuate the valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIGS. 1a and 1 b are schematic and diagrammatic illustrations of an engine valve actuator for an exhaust valve in accordance with an exemplary embodiment of the present invention; and

[0013]FIGS. 2a and 2 b are schematic and diagrammatic illustrations of an engine valve actuator for an intake valve in accordance with an exemplary embodiment of the present invention

DETAILED DESCRIPTION

[0014] An exemplary embodiment of an engine 20 is schematically and diagrammatically illustrated in FIG. 1a. Engine 20 includes an engine block 22 that defines a plurality of cylinders 23 (one of which is illustrated in FIG. 1a). A piston 26 is slidably disposed within cylinder 23 to reciprocate between a top-dead-center position and a bottom-dead-center position.

[0015] For the purposes of the present disclosure, engine 20 is described as a four stroke diesel engine. One skilled in the art will recognize, however, that engine 20 may be any other type of internal combustion engine, such as, for example, a gasoline or natural gas engine.

[0016] A connecting rod 27 connects piston 26 to a crankshaft (not shown). Piston 26 is coupled to the crankshaft so that a movement of piston 26 between the top-dead-center position and the bottom-dead-center position results in a rotation of the crankshaft. Similarly, a rotation of the crankshaft will result in a movement of piston 26 between the top-dead-center position and the bottom-dead-center position.

[0017] Engine 20 also includes a cylinder head 28. Cylinder head 28 is engaged with engine block 22 to cover cylinder 23 and define a combustion chamber 24. As shown in FIGS. 1a and 1 b, cylinder head 28 defines an exhaust passageway 30 that leads from an exhaust manifold opening 32 to an opening 31 into combustion chamber 24. In addition, as shown in FIGS. 2a and 2 b, cylinder head 28 defines an intake passageway 86 that leads from an intake manifold opening 87 to an opening 85 into combustion chamber 24.

[0018] As also shown in FIGS. 1a and 1 b, engine 20 includes an exhaust manifold 34 that may be engaged with cylinder head 28. Exhaust gases from combustion chamber 24 may be directed through exhaust passageway 30 to exhaust manifold 34. In addition, as shown in FIGS. 2a and 2 b, engine 20 includes an intake manifold 88 that may be engaged with cylinder head 28. Intake gases may be directed from intake manifold 88 through intake passageway 86 to combustion chamber 24.

[0019] As illustrated in FIGS. 1a and 1 b, an exhaust valve 65 having an exhaust valve element 68 may be disposed in opening 31. Exhaust valve element 68 is configured to selectively engage a seat 66 in opening 31. Exhaust valve element 68 may be moved between a first position where exhaust valve element 68 engages seat 66 to prevent a flow of fluid relative to opening 31 and a second position (as illustrated in FIGS. 1a and 1 b) where exhaust valve element 68 is removed from seat 66 to allow a flow of fluid relative to opening 31.

[0020] As shown in FIGS. 2a and 2 b, an intake valve 83 having an intake valve element 84 may be disposed in opening 85. Intake valve element 84 is configured to selectively engage a seat 67 in opening 85. Intake valve element 84 may be moved between a first position (as illustrated in FIG. 2b) where intake valve element 84 engages seat 67 to prevent a flow of fluid relative to opening 85 and a second position (as illustrated in FIG. 2a) where intake valve element 84 is removed from seat 67 to allow a flow of fluid relative to opening 85.

[0021] As illustrated in FIG. 1a, engine 20 also includes a cam shaft 39. Cam shaft 39 is operatively engaged with the crankshaft of engine 20. Cam shaft 39 may be connected with the crankshaft in any manner readily apparent to one skilled in the art where a rotation of the crankshaft will result in a corresponding rotation of cam shaft 39. For example, cam shaft 39 may be connected to the crankshaft through a gear train that reduces the rotational speed of cam shaft 39 to approximately one half of the rotational speed of the crankshaft.

[0022] As shown in FIGS. 1a and 1 b, an exhaust cam 40 may be engaged with cam shaft 39 to rotate with cam shaft 39. Exhaust cam 40 may include a first lobe 42 and a second lobe 44. As will be explained in greater detail below, the shape of the cam lobes on exhaust cam 40 will determine, at least in part, the actuation timing of exhaust valve element 68. One skilled in the art will recognize that exhaust cam 40 may include a greater or lesser number of cam lobes and/or the cam lobes may have different configurations depending upon the desired exhaust valve actuation timing.

[0023] As shown in FIGS. 2a and 2 b, an intake cam 80 may also be engaged with cam shaft 39 to rotate with cam shaft 39. Intake cam 80 may include a cam lobe 82. As will be explained in greater detail below, the shape of the cam lobe on intake cam 80 will determine, at least in part, the actuation timing of intake valve element 84. In the exemplary embodiment of FIGS. 2a and 2 b, the distance between the outer edge of cam lobe 82 varies between a first lobe position 100, a second lobe position 102, a third lobe position 104, and a fourth lobe position 106. One skilled in the art will recognize that intake cam 80 may include a greater number of cam lobes and/or a cam lobe having a different configuration depending upon the desired intake valve actuation timing.

[0024] Engine 20 also includes a series of valve actuation assemblies 36 (one of which is illustrated in each of FIGS. 1a, 1 b, 2 a, and 2 b). One valve actuation assembly 36 may be provided to move exhaust valve element 68 between the first and second positions. Another valve actuation assembly 36 may be provided to move intake valve element 84 between the first and second positions.

[0025] It should be noted that each cylinder 23 may include multiple intake openings 85 and exhaust openings 31. Each such opening will have an associated intake valve element 84 or exhaust valve element 68. Engine 20 may include two valve actuation assemblies 36 for each cylinder. The first valve actuation assembly 36 may be configured to actuate each of the intake valve elements 84 for each cylinder 23 and the second valve actuation assembly 36 may be configured to actuate each of the exhaust valve elements 68. Alternatively, engine 20 may include a separate valve actuation assembly to actuate each exhaust valve element 68 and each intake valve element 84.

[0026] Referring to FIGS. 1a and 1 b, each valve actuation assembly 36 includes a rocker arm 64 that includes a first end 76, a second end 78, and a pivot point 77. First end 76 of rocker arm 64 is operatively engaged with exhaust valve element 68 through a valve stem 70. Second end 78 of rocker arm 64 is operatively engaged with a valve actuator 38.

[0027] Valve actuation assembly 36 may also include a valve spring 72. Valve spring 72 may act on valve stem 70 through a locking nut 74. Valve spring 72 may act to move exhaust valve element 68 relative to cylinder head 28. In the illustrated embodiment, valve spring 72 acts to bias exhaust valve element 68 into the first position, where exhaust valve element 68 engages seat 66 to prevent a flow of fluid relative to opening 31.

[0028] As shown in FIG. 1a, valve actuator 38 may include a body member 46 that is slidably disposed in a bore 63 in a housing 62. Body member 46 includes a wall 53 that defines a chamber 50. Wall 53 includes a passageway 52 that provides a fluid conduit to chamber 50. Body member 46 also includes a seat 51.

[0029]FIGS. 1a and 1 b illustrate valve actuator 38 in connection with an exhaust valve. As shown, body member 46 is operatively engaged with exhaust cam 40. A rotation of exhaust cam 40 will cause first and second lobes 42 and 44 to engage body member 46 and move body member 46 relative to housing 62. The shape of first and second lobes 42 and 44 will determine the amount and the timing of the movement of body member 46 relative to housing 62.

[0030]FIGS. 2a and 2 b illustrate valve actuator 38 in connection with an intake valve. As shown, body member 46 is operatively engaged with intake cam 80. A rotation of intake cam 80 will cause cam lobe 82 to engage body member 46 and move body member 46 relative to housing 62. The shape of cam lobe 82 will determine the amount of movement of body member 46 relative to housing 62.

[0031] As also illustrated in FIG. 1a, each valve actuator 38 may include a piston 48 that is slidably disposed in chamber 50. Piston 48 may move between a first position, where piston 48 is engaged with seat 51 and a second position, where piston is removed from seat 51. A spring 60 may be disposed between seat 51 and piston 48 and act on piston 48 to move piston 48 towards the second position.

[0032] An actuator rod 49 is connected to piston 48. Actuator rod 49 engages second end of rocker arm 78. Movement of piston 48 and actuator rod 49 in the direction indicated by arrow 90 will cause rocker arm 78 to pivot and thereby move exhaust valve element 84 from the first position to the second position to allow a flow of fluid relative to opening 85.

[0033] Housing 62 may include a fluid passageway 54 that is connected to a tank 92. Tank 92 may contain a supply of low pressure fluid, such as, for example, an engine lubricating oil. Tank 92 may be part of a vehicle lubrication system, such as, for example, a lubrication rail or an oil sump.

[0034] Fluid passageway 54 is configured to align with passageway 52 in body member 46. Fluid may flow through fluid passageway 54 and passageway 52 to reach chamber 50. Similarly, fluid may flow from chamber 50 through passageway 51 to fluid passageway 54. Fluid passageway 54 may be configured to allow fluid to flow from chamber 50 into passageway 52 when body member 46 is at any point within housing 62.

[0035] A control valve 56 may be disposed in fluid passageway 54 to control fluid flow through fluid passageway 54. Control valve 56 has a first position where fluid is allowed to flow relative to fluid passageway 54. Control valve 56 also has a second position where fluid is prevented from flowing relative to fluid passageway 54. Control valve 56 may be an electronically controllable valve, such as, for example, a solenoid operated valve.

[0036] As also illustrated in FIG. 1a, a controller 58 may be connected to control valve 56 to control the position of control valve 56. Controller 58 may include an electronic control module that has a microprocessor and a memory. As is known to those skilled in the art, the memory is connected to the microprocessor and stores an instruction set and variables. Associated with the microprocessor and part of electronic control module are various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others.

[0037] Controller 58 may be programmed to control one or more aspects of the operation of engine 20. For example, controller 58 may be programmed to control valve actuation assembly 36, the fuel injection system, and any other function readily apparent to one skilled in the art. Controller 58 may control engine 20 based on the current operating conditions of the engine and/or instructions received from an operator.

[0038] Controller 58 may be further programmed to receive information, in the form of signals S₁, S₂, and S₃, from one or more sensors 94 that are operatively connected with engine 20. Each of the sensors 94 may be configured to sense one or more operational parameters of engine 20. For example, engine 20 may be equipped with sensors configured to sense one or more of the following: the temperature of the engine coolant, the temperature of the engine, the ambient air temperature, the engine speed, the load on the engine, and the intake air pressure.

INDUSTRIAL APPLICABILITY

[0039] The operation of the above-described engine valve actuation system will now be described with reference to the figures. The actuation of an exhaust valve will be described with reference to FIGS. 1a and 1 b and the actuation of an intake valve will be described with reference to FIGS. 2a and 2 b.

[0040] The operation of engine 20 will cause a rotation of the engine crankshaft, which will cause a corresponding rotation of cam shaft 39. As shown in FIG. 1a, the rotation of cam shaft 39 causes first lobe 42 of exhaust cam 40 to rotate into engagement with body member 46. In response, body member 46 will move in the direction indicated by arrow 90 relative to housing 62.

[0041] When control valve 56 is in the second position, fluid is prevented from flowing from chamber 50 through passageway 54. As body member 46 moves relative to housing 62, seat 51 will exert a force on the fluid trapped in chamber 50. Because the fluid cannot escape chamber 50, the fluid will exert a corresponding force on piston 48. The force of the fluid will cause piston 46 and body member 46 to move together in the direction indicated by arrow 90.

[0042] As piston 46 moves, actuator rod 49 engages and moves second end 78 of rocker arm 64. The movement of second end 78 of rocker arm 64 causes rocker arm 64 to pivot and move first end 76 in the opposite direction. The movement of first end 76 causes exhaust valve element 68 to disengage from seat 66 to allow a flow of fluid relative to opening 31. In this manner, exhaust valve element 68 may be opened to allow gases in combustion chamber 24 to flow through exhaust passageway 30 to exhaust manifold 34.

[0043] As first lobe 42 rotates out of engagement with body member 46, valve spring 72 will act on valve stem 70 to return exhaust valve element 68 into engagement with seat 66 to prevent fluid from flowing relative to opening 31. In addition, the force of valve spring 72 will cause rocker arm 64 to pivot and exert a corresponding force on actuator rod 49. The force on actuator rod 49 will act to move piston 49 and body member 46 so that body member 46 remains engaged with the surface of exhaust cam 40.

[0044] As illustrated in FIG. 1b, continued rotation of exhaust cam 40 will cause second lobe 44 to rotate into engagement with body member 46 and move body member 46 relative to housing 62. If control valve 56 is moved to the first position, fluid is allowed to flow from chamber 50 through fluid passageway 54. The movement of body member 46 relative to housing 62 will force fluid from chamber 50. Thus, body member 46 will move towards piston 48 as the fluid flows out of chamber 50 instead of transferring the force of body member 46 to piston 48.

[0045] Accordingly, piston 48 will remain motionless relative to housing 62 until seat 51 of body member 46 engages piston 48. The engagement of seat 51 with body member 46 will cause piston 48 to start moving relative to housing 02. The movement of piston 48 and actuator rod 49 will cause rocker arm 64 to pivot and thereby move exhaust valve element 68 out of engagement with seat 66.

[0046] As second lobe 44 rotates out of engagement with body member 46, valve spring 72 will act to move piston 48 and body member 46 to remain engaged with exhaust cam 40. When valve spring 72 is fully extended, spring 60 will act to separate body member 46 from piston 48. The movement of body member 46 away from piston 48 will create a vacuum that acts to draw fluid into chamber 50 through fluid passageway 54.

[0047] One skilled in the art will recognize that the shapes of the lobes on exhaust cam 40 may be configured to implement any valve actuation timing. In the exemplary embodiment of FIGS. 1a and 1 b, first and second lobes 42 and 44 are configured to implement an “engine braking” cycle. Second lobe 44 may be oriented relative to cam shaft 39 to engage body member 46 to move exhaust valve element 68 to the second position when piston 26 is moving from a bottom-dead-center position to a top-dead-center position in an exhaust stroke. Second lobe 44 may be configured to engage body member 46 and actuate exhaust valve element 68 regardless of the position of control valve 56.

[0048] First lobe 42 may be oriented relative to cam shaft 39 to engage body member 46 when piston 26 is moving towards the top-dead-center position in a compression stroke. First lobe 42 may be configured so that first lobe 42 only actuates exhaust valve element 68 when control valve 56 is in the second position. Thus, when control valve 56 is in the first position and fluid is allowed to flow from chamber 50, first lobe 42 will not cause seat 51 to engage piston 48 and exhaust valve element 68 will not be actuated as piston 26 moves towards the top-dead-center position of the compression stroke. In other words, the engine braking cycle may be implemented by moving control valve 56 to the second position and disabled by moving control valve 56 to the first position.

[0049] Controller 58 may selectively enable or disable the engine braking cycle based on the sensed operating conditions. For example, if controller 58 determines that engine 20 is accelerating or operating under steady state conditions, controller 58 may move control valve 56 to the first position to disable engine braking. If, however, controller 58 determines that the vehicle is slowing down, such as in response to an operator applying the brakes, controller 58 may move control valve 56 to the second position to enable engine braking.

[0050] As shown in FIGS. 2a and 2 b, rotation of cam shaft 39 will also cause a rotation of intake cam 80 and cam lobe 82. Body member 46 will ride along the surface of intake cam 80 until cam lobe 82 rotates into engagement with body member 46 at first lobe position 100. Cam lobe 82 may be oriented to engage body member 46 as piston 26 is near or approaching a top-dead-center position in an exhaust stroke.

[0051] When control valve 56 is in the second position and is preventing fluid from escaping chamber 50, the rotation of cam lobe 82 from first lobe position 100 to second lobe position 102 will move body member 46 and piston 48 relative to housing 62 to thereby pivot rocker arm 64 and disengage intake valve element 84 from seat 67. In this manner, intake valve 83 may be opened to allow intake air to flow into compression chamber 24 from intake manifold 88 as piston 26 begins the intake stroke. When cam lobe 82 rotates past fourth lobe position 106, valve spring 72 returns intake valve 83 to the first position and pivots rocker arm 64 to move body member 46 and piston 48 relative to housing 62.

[0052] Fourth lobe position 106 of cam lobe 82 may be configured to implement a “late intake Miller cycle.” With this configuration, cam lobe 82 is adapted such that fourth lobe position 106 will rotate out of engagement with body member 46 thereby allowing intake valve element 84 to return to the first position after piston 26 completes a first portion of a compression stroke. Thus, with control valve 56 in the second position, cam lobe 82 will implement a late intake Miller cycle.

[0053] It should also be noted that intake valve 83 may be closed after third lobe position 104 rotates past body member 46 by moving control valve 56 to the first position to allow fluid to escape from chamber 50. This will remove the fluid link between body member 46 and piston 48. Accordingly, valve spring 72 will act to pivot rocker arm 64, thereby closing intake valve 83 and moving piston 48 into engagement with seat 51 of body member 46. In this manner, intake valve 83 may be closed “early” to reduce the amount of air that enters the respective combustion chamber when the engine requires less air under the particular operating conditions.

[0054] The late intake Miller cycle may be disabled by moving control valve 56 to the first position to allow fluid to escape chamber 50. As cam lobe 82 rotates into engagement with body member 46 at first lobe position, body member 46 will move relative to housing 62 and piston 48 and force fluid out of chamber 50. As cam lobe 82 continues to rotate, seat 51 of body member 46 will engage and move piston 48 to rotate rocker arm 64 open intake valve 83. Seat 51 of body member 46 may engage piston when second cam position 102 engages body member 46. Valve spring 72 will act to close intake valve 83 when third lobe position 104 rotates past body member 46. Third lobe position 104 may be positioned so that intake valve 83 closes as piston 26 is at or near the bottom-dead-center position of the intake stroke.

[0055] The opening of intake valve 83 and the amount of lift of intake valve 83 may be varied by moving control valve 56 to the second position to stop the escape of fluid from chamber 50 when cam lobe 82 rotates between first lobe position 100 and second lobe position 102. When control valve 56 is moved to the second position, the fluid remaining in chamber 50 will link body member 46 to piston 48. Continued rotation of cam lobe 82 will cause body member 46 and piston 48 to move relative to housing 62 to thereby pivot rocker arm 64 and open intake valve 83. However, as the amount of fluid in chamber 50 is reduced, intake valve 83 will be a smaller distance than had control valve 50 been in the second position before first lobe position 100 engaged body member 46. In this manner, the time at which intake valve 83 is opened and the amount of lift of intake valve 83 may be varied.

[0056] Controller 58 may control the position of control valve 56 based on the sensed operating conditions. For example, controller 58 may leave control valve 56 in the second position to implement the late intake Miller cycle when the controller determines that the engine is operating under steady state conditions. If, however, controller 58 determines that engine 20 is experiencing a transient condition, controller 58 may move control valve 56 between the first and second positions to disable the late intake Miller cycle.

[0057] As will be apparent from the foregoing description, the present invention provides an engine valve actuator that may use low pressure fluid to selectively alter the actuation timing and lift distance of the intake and/or exhaust valves of an internal combustion engine. The actuation timing and lift distance of the engine valves may be varied to improve the performance of the engine based on the sensed operating conditions of the engine. For example, the actuation timing and lift distance of the intake valves may be controlled to allow varying amounts of air to enter the respective combustion chambers, depending upon the operating conditions of the engine, implement a late intake Miller cycle when the engine is operating under normal operating conditions. In addition, the actuation of the exhaust valves may be controlled to implement an engine braking cycle. Thus, the engine valve actuator may allow for improvements in both engine efficiency and emission generation.

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed engine valve actuator without departing from the scope of the present disclosure. Other embodiments of the engine valve actuator will be apparent to those skilled in the art from consideration of the specification and practice of the device disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 

What is claimed is:
 1. An engine valve actuation system, comprising: an engine valve having a valve element; a rocker arm having a pivot point, a first end, and a second end, the first end of the rocker arm operatively engaged with the engine valve; and a valve actuator having: a body member having a chamber adapted to receive a fluid, a seat, and a passageway adapted to conduct fluid into and out of the chamber; a piston slidably disposed in the chamber of the body member and operatively engaged with the second end of the rocker arm; and a control valve connected to the passageway and having a first position where fluid is allowed to flow relative to the passageway to allow the body member to move relative to the piston until the seat moves into engagement with the piston to thereby move the piston to pivot the rocker arm and actuate the engine valve, the control valve having a second position where fluid is prevented from flowing relative to the passageway so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and actuate the engine valve while the piston is separated from the seat by an amount of fluid.
 2. The actuator of claim 1, further including a spring acting on the piston to bias the piston away from the seat of the body member.
 3. The actuator of claim 2, wherein the spring is disposed in the chamber of the body member.
 4. The actuator of claim 1, wherein the body member includes a wall defining the chamber and the passageway is disposed in the wall adjacent the seat.
 5. The actuator of claim 1, further including a controller adapted to move the control valve between the first and second positions.
 6. The actuator of claim 1, further including a housing having a bore and wherein the body member is slidably disposed in the bore.
 7. The actuator of claim 6, wherein the housing includes a second passageway adapted for selective communication with the passageway in the body member.
 8. A method of actuating a valve in an engine, comprising: operating a cam assembly to move a body member between a first position and a second position, the body member having a chamber adapted to slidably receive a piston that is operatively connected to a valve element through a rocker arm; directing a fluid into the chamber in the body member; sensing an operating parameter of the engine; preventing the fluid from leaving the chamber when the sensed operating parameter indicates that the engine is experiencing a first operating condition, the fluid in the chamber linking the body member with the piston so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and thereby actuate the valve; and allowing the fluid to leave the chamber when the sensed operating parameter indicates that the engine is experiencing a second operating condition, the escaping fluid allowing the body member to move relative to the piston until the seat engages the piston to pivot the rocker arm and thereby actuate the valve.
 9. The method of claim 8, further including moving a control valve to a first position to allow the fluid to flow relative to a passageway to leave the chamber.
 10. The method of claim 9, further including moving the control valve to a second position to prevent fluid from flowing relative to the passageway.
 11. The method of claim 8, wherein the first operating condition is one of a first set of operating conditions and the second operating condition is one of a second set of operating conditions.
 12. An engine system, comprising: a cam shaft; a cam assembly operatively connected to the cam shaft and adapted to rotate with the cam shaft; an engine block defining a cylinder having a combustion chamber; a cylinder head defining a first passageway connecting one of an intake manifold and an exhaust manifold with the combustion chamber; an engine valve having a valve element disposed in the first passageway and moveable between a first position where the valve element prevents a flow of fluid relative to the first passageway and a second position where the valve element allows a flow of fluid relative to the first passageway; a rocker arm having a pivot point, a first end, and a second end, the first end of the rocker arm operatively engaged with the engine valve; and a valve actuator having: a body member having a chamber adapted to receive a fluid, a seat, and a second passageway adapted to conduct fluid into and out of the chamber; a piston slidably disposed in the chamber of the body member and operatively engaged with the second end of the rocker arm; and a control valve connected to the second passageway and having a first position where fluid is allowed to flow relative to the second passageway to allow the body member to move relative to the piston until the seat moves into engagement with the piston to thereby move the piston to pivot the rocker arm and move the engine valve towards the second position, the control valve having a second position where fluid is prevented from flowing relative to the second passageway so that movement of the body member causes a corresponding motion of the piston to pivot the rocker arm and move the engine valve towards the second position while the piston is separated from the seat by an amount of fluid.
 13. The engine of claim 12, further including a valve spring acting on the valve element to move the valve element towards the first position.
 14. The engine of claim 12, further including a spring acting on the piston to move the piston away from the seat of the body member.
 15. The engine of claim 12, wherein the body member includes a wall defining the chamber and the passageway is disposed in the wall adjacent the seat.
 16. The engine of claim 12, further including a controller adapted to move the control valve between the first and second positions.
 17. The engine of claim 16, further including a sensor adapted to sense an operating parameter of the engine and wherein the controller moves the control valve to the first position when the sensed operating parameter indicates that the engine is operating in one of a first set of operating conditions.
 18. The engine of claim 17, wherein the controller moves the control valve to the second position when the sensed operating parameter indicates that the engine is operating in one of second set of operating conditions.
 19. The engine of claim 12, wherein the cam assembly includes a cam lobe adapted to move the body member from the first position to the second position.
 20. The engine of claim 19, wherein the cam lobe is configured to move the seat of the body member into engagement with the piston to move the piston and the valve element towards the second position when the control valve is in the first position.
 21. The engine of claim 19, wherein the cam lobe is configured such that the seat of the body member does not engage the piston when the control valve is in the first position.
 22. The engine of claim 12, wherein the valve element is an exhaust valve and wherein the cam assembly is adapted to open the exhaust valve when the piston is moving through an exhaust stroke when the control valve is in the first position, the cam assembly being further adapted to open the exhaust valve when the piston is moving through the exhaust stroke and when the piston is at or near a top dead center position of a compression stroke when the control valve is in the second position.
 23. The engine of 12, wherein the valve actuator further includes a housing having a bore and wherein the body member is slidably disposed in the bore.
 24. The engine of claim 23, wherein the housing includes a second passageway adapted for selective communication with the passageway in the body member. 